COMPARISON OF 2 ANTIGEN TESTS AND THE MODIFIED KNOTT TEST FOR DETECTION OF CANINE HEARTWORM AT DIFFERENT WORM BURDENS

In a retrospective study, the relative sensitivities of the two most commonly used heartworm antigen tests, DiroCHEK(R) (Synbiotics Corporation, San Diego, Calif.) and CITE Semi-Quant(TM) (Idexx Corporation, Westbrook, Maine), were compared with that of a concentration test for microfilariae (modified Knott's technique) in dogs with heartworm burdens that ranged from very low to high. Both antigen tests were significantly more sensitive than the Knott's test at all worm burdens (1-2 worms, 2-5 worms, 6-10 worms, 11-20 worms, and > 20 worms). The advantage in sensitivity of the antigen tests over the Knott's test ranged from as high as 45% at the lowest worm burdens to as little as 10% at the highest worm burdens. When both an antigen test and the Knott's test were run in tandem, there was no statistically significant improvement in sensitivity over that of the antigen test alone, although the Knott's test did detect three infections (0.5%) not detected by DiroCHEK and four infections (1.0%) not detected by CITE.